METHOD AND DEVICE FOR OPTICAL QUALITY CONTROL IN LASER DECLARATION WELDING

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for optical quality control in laser cladding. It also relates to a device for carrying out such a method. BACKGROUND OF THE INVENTION

[0002] In laser material deposition, also known as "laser cladding," a high-energy laser beam is directed through a focusing lens onto the surface of a workpiece to be coated. The energy thus introduced into the workpiece causes local melting of the material, creating a molten pool on the surface at a processing spot. A powdered coating material, such as a metal powder, is applied to the molten pool in the processing spot. For example, a gas stream transports the fine metal powder along a laser head that houses the focusing lens. The gas stream containing the metal powder exits through small gas outlet nozzles onto the processing spot and then deposits the metal powder in the molten pool.Due to the high temperatures prevailing there, the metal powder also melts and bonds with the workpiece, creating a coating of the coating material. In addition to metal powder, ceramic powder materials, especially hard materials, can also be used as coating materials. During this process, the laser head with the gas outlet nozzles and the workpiece move relative to each other; for example, the laser head is moved over the surface of the workpiece to be coated. High-speed laser cladding works according to the same principle, but with a much higher laser beam power and a high relative travel speed between the laser head and the workpiece. STATE OF THE ART

[0003] From EP 1 036 856 B1 a method for quality assurance in thermal spraying is known, in which a plasma jet directed onto a workpiece surface to be coated, into which a powdery coating material is introduced from the side, is observed from the side by means of an image capture device.In the images thus acquired, at least one area of ​​the same intensity and / or at least one area within a specific intensity interval is assigned to one or more symmetrical geometric surface bodies by means of computational processing and / or alienation, wherein the symmetrical geometric surface body or bodies are recorded as a data set or data sets on the basis of features characteristic of the respective geometric shape and at least one feature of the thermal spraying process which influences the quality of the spray layer is recorded, controlled and / or monitored via this data set or these data sets.

[0004] In this known process, quality control is not performed on the coated workpiece, but rather on the plasma beam enriched with coating material that creates the coating. This quality control is thus performed indirectly, not directly.

[0005] US 2017 / 0151628 A1 describes a device for temperature detection in additive manufacturing and for controlling additive manufacturing, as well as a method for using such a device. A spectrophotometric sensor detects the material melt generated by a laser beam during additive manufacturing. The light emitted by the melt is detected by the sensor, and the temperature is determined from this using spectral analysis. A two-dimensional temperature profile of the observed melt is created. The color temperature of the light emitted by the melt is used to determine the temperature. The two-dimensional temperature profile of the observed melt spot determined in this way is used to determine iso-temperature lines.These iso-temperature lines form the geometric shape of the melt spot and, together with an iso-temperature profile resulting from different iso-temperature lines, serve as the control data for the energy delivered to the laser. According to this teaching, the light emitted by the melt spot is received by a spectrophotometric sensor, and a two-dimensional temperature profile of the melt spot is created from this. Iso-temperature lines are then created from this temperature profile, which are then used to control the laser.

[0006] US 6,995,334 B1, which forms the basis for the preamble of the independent claims, shows and describes both a method and a device for optical quality control for laser cladding. During laser cladding, a melt pool formed on a workpiece is observed with an image capture device in such a way that radiation emanating from the melt pool is first filtered and then captured by the image capture device. At least one property of the melt pool is then compared with a corresponding stored property of a target melt pool, and the laser intensity is adjusted based on the deviations determined in this comparison. The corresponding property is the width of the melt pool, assuming that the melt pool is substantially circular.

[0007] DE 10 2011 103 282 A1 shows and describes a method for monitoring the processing of a workpiece with a high-energy processing beam, as well as a related device. Using an image capture device, the diameter of the impact point of the high-energy beam on the workpiece to be processed is determined and stored. In a next step, it is checked whether the acquired image data, i.e., the recorded diameter of the impact point, matches a stored target value. If a deviation is detected, the process parameters are subsequently adjusted. PRESENTATION OF THE INVENTION

[0008] The object of the present invention is therefore to provide an improved method and an associated device for optical quality control of a thermal coating process, with which improved quality control can be carried out during laser deposition welding.

[0009] The part of the problem directed to the method is solved by a method having the features of claim 1. The part of the problem directed to the device is solved by a device having the features of claim 9.

[0010] A method according to the invention for optical quality control during laser cladding, wherein in the process of laser cladding the surface of a workpiece to be coated is melted by means of a high-energy laser beam directed onto a processing spot on the surface and focused by focusing optics onto an impact point on the surface, wherein a relative movement occurs between the laser beam and the workpiece, wherein a melt pool is generated by the laser beam in the processing spot, and wherein a powdered coating material is applied to the melt pool in the processing spot, comprises the following steps: a) detecting the electromagnetic radiation emitted as light by the molten pool by means of an image capture device, wherein the brightness of the emitted light represents the intensity of the emitted electromagnetic radiation; b) forwarding the detected image information of the molten pool to an image evaluation unit and controlling and / or monitoring at least one parameter of the laser deposition welding process that influences the quality of the coating by means of a process control device on the basis of the detected image information; c) computationally determining the location data of at least one area of ​​equal intensity and / or of at least one area within a specific intensity interval in the detected image information to form a contour of the area; d) assigning at least one symmetrical, elliptical surface body to the at least one area of ​​equal intensity by approximating an ellipse to the contour of the area;e) determining features characteristic of the geometric shape of the at least one symmetrical, elliptical surface body; f) storing the characteristic features of the at least one symmetrical, elliptical surface body as a data set in a data storage device; and g) detecting, controlling, and / or monitoring at least one parameter of the laser deposition welding process that influences the quality of the coating by means of a process control device based on the data of the characteristic features of the at least one symmetrical, elliptical surface body. ADVANTAGES

[0011] By directly monitoring the quality of the welding process on the surface of the workpiece to be coated, parallel to the workpiece processing being performed, using the image capture device, a more precise and reliable quality assessment can be performed than with only indirect monitoring. The invention directly compares the image signal captured by the image capture device with the intensity of the received electromagnetic radiation, without the need for a temperature measurement.The method according to the invention makes it possible to examine the welding process, i.e., the melting of the powdered coating material in the melt pool, directly during workpiece processing using the image capture device and to analyze it as indicated, for example, in step g) by comparing the determined characteristic features with corresponding target values ​​for these features, which can be stored in a memory device. Preferably, individual parameters of the laser deposition welding process can also be controlled and / or regulated in at least one step following step g).

[0012] In the method of the invention, the focus is therefore not on a scientifically precise melt pool measurement with the generation of physical values ​​such as the determination of temperature or speed, as would be useful for research and development purposes, but on a fundamental process analysis with the simplified result "OK" or "not OK", which is entirely sufficient for use in the series coating of workpieces by means of laser deposition welding.

[0013] This utilizes the effect that the melt pool develops effects of varying intensity depending on certain material properties of the melting material. One such effect can be, for example, the emission of electromagnetic radiation, such as visible or invisible light. In this latter example, the melt pool glows more intensely, i.e. brighter (at higher temperature) or less intensely, i.e. less bright (at lower temperature), depending on the temperature in the melt pool. Areas of different brightness thus represent areas of different temperature. The image captured by the image capture device therefore has at least one area of ​​the same intensity (= same brightness) and / or at least one area within a certain intensity interval (= brightness interval), which forms the basis for further analysis.The use of the effect comprising the emission of light can be designed in such a way that this use is directed to one or more frequency ranges (= colours) of the light emitted by the melt pool.

[0014] The computational determination of location data, for example, the coordinates of each location, of at least one region of equal intensity, or of the region within an identity interval, yields a curve or band-like surface, also referred to below as an "isointensity line," to which a symmetrical surface is mathematically assigned. In the static case, this surface is circular, and in the moving case (relative motion between the laser head and the workpiece), it is, for example, elliptical.

[0015] The computational method used is a threshold-oriented contour search followed by an approximation of a geometric figure to this contour. The threshold-oriented contour is the isointensity line. According to the invention, the geometric figure resulting from such an approximation is an ellipse whose characteristic features are the position (spatial coordinates - x, y) of the center, the respective radius of the two main axes, and the orientation of the main axes around a vertical axis passing through the center. These characteristic features, in this example the five property values ​​of the ellipse mentioned above, represent a simplified result of the image analysis, which can then be used for computational comparison with a standard.

[0016] This determination of a simplified result with the method of the invention based on the characteristic features of the at least one symmetrical surface simplifies and accelerates the analysis of the image(s) captured by the image capture device, since only the characteristic features (e.g., the center position and diameter of a circle or the center position, radii, and orientation of an ellipse) of the symmetrical surface need to be compared with a predetermined standard. The method according to the invention is therefore particularly suitable for high-speed laser cladding with high relative speeds between the laser head and the workpiece.

[0017] Further preferred and advantageous features of the method according to the invention are the subject of subclaims 2 to 8.

[0018] Preferably, several individual images are taken during the interval, each with a short shutter speed. Since the molten pool undulates during the laser deposition welding process and thus the intensity of the captured image information (e.g., the brightness in the selected spectral range) fluctuates greatly, the individual captured images can vary greatly in terms of the image information they contain. In addition, it may happen that the particles of the powdered coating material blown onto or into the molten pool partially bounce off the surface of the molten pool or fly through the image; such a single image is also less suitable for the type of quality control according to the invention. Therefore, preferably several images are taken during an interval (e.g., 1 to 100 images), and the image information contained therein is averaged.This results in a virtually stable resulting image with representative intensity values ​​and without any interfering individual particles that locally distort the image brightness. Such a resulting image, formed from a plurality of individual images with averaged intensity values ​​and / or their averaged location data or with averaged data of the characteristic features, is particularly suitable for evaluation using the method according to the invention.

[0019] A particularly preferred development of the method is one in which the image information of the melt pool acquired in step a) is stored in an image information memory in a subsequent step a'), and in which steps a) and a') are then repeated several times. After a predetermined number of repetitions, the image information is averaged in a step a"), and the subsequent method steps are carried out using this averaged image information.

[0020] The image information acquired in step a) consists, for example, of intensity values ​​(e.g., brightness values) assigned to a pixel of the rasterized recorded image; this creates an intensity value matrix. With each repetition, the newly determined intensity values ​​are added to the respective previously determined intensity value or the respective intensity value sum. After all repetitions have been completed, an average intensity value is calculated for each pixel. This then creates a resulting image with the averaged intensity values ​​as image information, which forms the basis for the subsequent process steps. In this way, the wobble of the melt spot is optically "smoothed."

[0021] Preferably, steps a) to g) are repeated at intervals. This ensures virtually permanent quality control.

[0022] It is also advantageous if steps a) to f) are repeated at intervals and if, in step g), the data of the characteristic features of the at least one symmetrical surface body determined over a period of several intervals are first averaged.

[0023] In a preferred alternative, steps a) to c) are repeated at intervals, wherein the location data of the at least one area of ​​equal intensity are averaged and wherein steps d) to g) are carried out on the basis of the at least one averaged area of ​​equal intensity.

[0024] According to a preferred embodiment of the method of the invention, which can be combined with other embodiments of the invention, at least one spectral range of visible light and / or ultraviolet light and / or infrared light is detected in step a).

[0025] It is advantageous if steps a) to f) are carried out for several spectral ranges and if step g) is carried out on the basis of the data of the characteristic features of the at least one symmetrical surface body determined in the several spectral ranges. Liquid metal radiates in different wavelengths and thus in different colors depending on the material composition. Carrying out steps a) to f) for several spectral ranges, whereby a comparison of the determined characteristic features with assigned target values ​​is preferably carried out for each of the spectral ranges, extends the evaluation options to material-specific parameters and the resulting findings. In this way, the material composition can be included in quality control as a further process variable.

[0026] A preferred embodiment of the method of the invention, which can be combined with other embodiments of the invention, is particularly advantageous, according to which a relative movement occurs between the laser beam and the workpiece and wherein the geometric shape of the at least one symmetrical surface body is an ellipse. This variant is particularly suitable for high-speed laser cladding, i.e. for high-speed laser deposition welding. The high relative movement between the laser head and the workpiece leads to the formation of an oval melt pool that is elongated in the direction of movement, and the location data of the at least one area of ​​equal intensity, particularly when observed over several intervals, assume an elliptical shape whose longer radius runs in the direction of movement.

[0027] The device according to the invention for optical quality control during the laser deposition welding process is provided with an image capture device, an image evaluation unit, a data storage device and a process control device and is designed to carry out a method according to the invention, wherein the image capture device is designed to capture electromagnetic radiation emitted as light by a melt pool formed in a processing spot. It is characterized in that the image evaluation unit is designed to determine, on the basis of the captured image information, the location data of at least one area of ​​equal intensity and / or of at least one area within a specific intensity interval in the captured image information to form a contour of the area in order to assign at least one symmetrical,elliptical surface body by approximating an ellipse to the contour of the area in order to determine characteristic features of the geometric shape of the at least one symmetrical, elliptical surface body and to store the characteristic features of the at least one symmetrical, elliptical surface body as a data set in a data storage device, and that the process control device is designed to detect, control and / or monitor the at least one parameter of the laser deposition welding process influencing the quality of the coating by means of the data of the characteristic features of the at least one symmetrical, elliptical surface body.

[0028] Further preferred and advantageous design features of the device according to the invention are the subject of subclaims 9 and 10.

[0029] It is advantageous if the image capture device is an electronic camera.

[0030] Preferably, an output mirror is provided in the radiation path of the laser beam, which output mirror couples out the light emitted from the melt pool along the radiation path of the laser beam, opposite to its propagation direction, from the radiation path of the laser beam and guides it to the image capture device.

[0031] However, the radiation path of the image capture device is not limited to this; it can also run independently and separately from the radiation path of the laser beam, for example in the case of an image capture device arranged laterally and directed obliquely from above directly onto the melt pool.

[0032] Preferred embodiments of the invention with additional design details and further advantages are described and explained in more detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] It shows: Fig. 1 is a partially sectioned schematic view of a device according to the invention and Fig. 2 is an image of a melt pool captured by the image capture device with an ellipse displayed as an associated symmetrical surface body. PRESENTATION OF PREFERRED EMBODIMENTS

[0034] Fig. 1shows a partially sectioned schematic representation of a device for optical quality control during laser cladding. This device comprises a laser head 1 with a laser light source 10, which is arranged, for example, inside a housing 12 of the laser head 1. The housing 12 comprises an upper cylindrical section 12', in the upper region of which the laser light source 10 is provided, and a lower conical section 12", which tapers downwards from the cylindrical section 12' and which has a central light passage opening 13 at its lower end in the region of the tip of the cone formed thereby. Alternatively, the laser light source can also be arranged outside the laser head 1 and connected to the laser head 1 for light transmission via a suitable light-guiding device.

[0035] The laser light source 10 is provided with a light exit 11 at its lower end, directed toward the light passage opening 13. When the laser light source is switched on, a laser beam 14 emerges downwards (radiation direction A) coaxial with the Z axis of the cylindrical housing section 12'. The laser beam 14 passes through an output mirror 15 positioned at 45° to the Z axis and then through a focusing optics 16, where it is focused. The focused laser beam 14 exits the housing 12 through the passage opening 13 and strikes the surface 20 of, for example, a metal workpiece 2 at an impact point 22.

[0036] The laser beam focused by the focusing optics 16 onto the point of impact 22 of the laser beam 14 on the surface 20 of the workpiece 2 heats the surface in a surface area referred to as the processing spot 24, which includes the point of impact 22 of the laser beam 14 on the surface 20 of the workpiece 2 as well as the area surrounding the point of impact 22, which is also heated by thermal conduction. In the processing spot 24, which in the ideal static case forms a circle around the point of impact 22, the surface 20 of the workpiece 2 is melted by the focused laser beam 14, creating a melt pool 26 made of the material of the workpiece 2.

[0037] Since the laser head 1 moves relative to the workpiece 2 along the surface 20 of the workpiece 2, which is symbolized by the movement arrow X, with the distance between the surface 20 and the light passage opening 13 of the laser head 1 remaining essentially constant, the melt pool 26 forms an elongated-oval shape because the melt pool 26 does not immediately solidify as the laser beam 14 continues to move over the surface 20 of the workpiece 2. In the figures, the longitudinal dimension e 1 of this elongated-oval shape is indicated in the direction of movement X. Alternatively, the workpiece 2 can also move relative to the then stationary laser head 1.

[0038] The laser head 1 is further provided with a powder feed device 3, which in the example shown consists of two feed tubes 30, 32 and a feed line 34 connected to the feed tubes 30, 32. The feed tubes 30, 32 run largely parallel to the cylinder axis Z through the cylindrical section 12' of the housing 12 from top to bottom and exit in the area of ​​the conical section 12" of the housing 12. Below the conical section 12" of the housing 12, the two feed tubes 30, 32 each have a lower section 30', 32' directed obliquely to the cylinder axis Z, each forming a nozzle opening 30", 32" at the lower end. Even if in Fig. 1 only two feed pipes 30, 32 are provided, the invention is not limited thereto; only one feed pipe or more than two feed pipes may be provided.

[0039] A gas enriched with a powdered coating material is transported through the feed line 34 and the feed tubes 30, 32, which exits at the lower nozzle openings 30", 32", so that the powder particles contained therein are blown as a powder jet 36, 38 of the coating material onto the molten pool 26 on the surface 20 of the workpiece 2. The powder particles striking there melt due to the high temperatures generated there by the laser beam 14 and thus fuse in the molten pool 26 with the molten material of the surface 20 of the workpiece 2. Due to the relative movement between the laser head 1 and the workpiece 2, the entire surface 20 of the workpiece 2 to be coated is coated with the powdered material.

[0040] The device 1 according to the invention further comprises an image capture and evaluation unit 4, which comprises an image capture device 40, for example an electronic camera, an image evaluation unit 42 connected to the image capture device 40 for data transmission, with a data storage device 44 connected thereto and connected for data transmission, and a process control device 46, which is also connected to the image evaluation unit 42 for data transmission and is designed to control and / or regulate process parameters of the device according to the invention for optical quality control, in particular of the laser head 1 and / or the powder feed device 3.

[0041] The image capture device 40 is provided with a camera lens 41 that receives light 47, preferably in the visible wavelength range, emitted by the melt pool 26. In the example shown, this emitted light 47 travels along the beam path of the laser beam 14 in a direction B opposite to the propagation direction A of the laser beam 14 and passes through the focusing lens 16, after which it strikes the output mirror 15, where it is decoupled from the beam path of the laser beam 14 and deflected to the side, where it then exits the housing 12 of the laser head 1 through a lateral light exit opening 17. The decoupled light 47 is then directed to the camera lens 41 of the image capture device 40. The image capture device 40 thereby captures an image of the melt pool 26 on an image sensor (not shown).Depending on the positioning and orientation of the image capture device 40, the beam path directed to the image capture device can also run separately from the beam path of the laser beam 14, for example on a direct path between the melt pool 26 and the image capture device 40.

[0042] This camera image is in Fig. 2 The view from above through the light passage opening 13 in the housing 12 onto the surface 20 of the workpiece 2 to be coated is shown in the image frame R. The melt pool 26 can be seen there, the irregular outer contour of which does not represent a sharp boundary between the solid material of the workpiece 2 and the molten material, but whose boundary is wavy due to the temperature distribution and the movement of the laser head 1. Fig. 2The point of impact 22 of the laser beam 14 on the surface 20 of the workpiece 2 is shown schematically, which point of impact moves in the direction of the arrow X relative to the workpiece 2. The image information of the recorded melt pool 26 captured by the image capture device 40 - this is the image information from the Fig. 2 displayed image within frame R - is forwarded to the image evaluation unit 42. There, areas of equal intensity, for example areas of equal image brightness, are determined in the entire visible light spectrum or in partial spectra of some colors, and from this information, a curve or band-like surface, also referred to below as isointensity line 28, of the locations of equal intensity or equal intensities of an intensity range, for example equal brightness, is determined mathematically.

[0043] This isointensity line 28, which is Fig. 2schematically represented by a dashed line, an ellipse E is assigned as a symmetrical surface body which, in its orientation (long ellipse axis e' 1 and short ellipse axis e' 2 ) and in its area, is closest to the dashed isointensity line 28. The characteristic features of this ellipse E are, for example, its major axis e' 1 and its minor axis e' 2 .

[0044] This from the picture of the Fig. 2 derived characteristic features, which include not only the length of the major axis e' 1 and the minor axis e' 2 of the ellipse E, but also their orientation around the center M of the ellipse E in the plane of the surface 20 (plane of the drawing in Fig. 2) are then compared with comparable characteristic features stored in the data storage device 44. These stored characteristic features were determined at an earlier point in time in a test carried out under optimal laboratory conditions and reflect the ideal process conditions for laser material deposition. Due to the deviations of the characteristic features of the ellipse E from the ideal characteristic features stored in the data storage device 44, individual parameters such as the intensity of the laser beam, the distance of the light passage opening 13 of the laser head 1 to the surface 20 of the workpiece 2 and / or the quantity and speed of the particle beam 36, 38 emerging from the nozzle openings 30", 32" can now be adjusted or readjusted.

[0045] In the example shown, in process step d), process-describing ellipses are approximated into the images of the ongoing laser cladding process. In process step g), the ellipse parameters obtained in step e) are compared with previously defined reference parameters that describe an optimal process. This comparison can be used to detect the following process variables or to draw conclusions about them: Process stability and consistency of the laser cladding process Change in the applied process power Heat input into the workpiece in the area of ​​the impact point 22 Heat dissipation from the melt pool into the surrounding workpiece area Changes in powder type and powder flow Changes in the process temperature.

[0046] In this way, the quality of the coating applied to the surface 20 of the workpiece 2 can be controlled using simple parameters and the laser deposition welding process can be controlled or regulated.

[0047] Reference symbols in the claims, the description and the drawings serve only to improve the understanding of the invention and are not intended to limit the scope of protection. List of reference symbols

[0048] They refer to: 1 Laser head 2 Workpiece 3 Powder feed device 4 Evaluation unit 10 Laser light source 11 Light exit 12 Housing 12' Upper cylindrical housing section 12" Lower conical housing section 13 Light passage opening 14 Laser beam (processing beam path) 15 Output mirror 16 Focusing optics 17 Light exit opening 20 Surface 22 Impact point 24 Processing spot 26 Melt pool 28 Isointensity line 30 Feed tube 30' Lower section 30" Nozzle opening 32 Feed tube 32' Lower section 32" Nozzle opening 34 Feed line 36 Powder jet 38 Powder jet 40 Image capture device 41 Camera optics 42 Image evaluation unit 44 Data storage device 46 Process control device 47 Light (Observation beam path) ADirection of propagation BRange opposite to the direction of propagation EEllipse e 1 Longitudinal dimension of the melt pool in the direction of movement e' 1 Long axis of the ellipse e' 2 Short axis of the ellipse MCenter of the ellipse RImage frame XDirection of movement ZZCylinder axis

Claims

1. Method for optical quality control in laser deposition welding, wherein in the process of laser deposition welding the surface (20) of a workpiece (2) to be coated is melted by means of a high-energy laser beam (14) directed onto a processing spot (24) of the surface (20) and focussed by focussing optics (16) onto a point of impact (22) on the surface (20), wherein a relative movement takes place between the laser beam (14) and the workpiece (2), wherein a molten pool (26) is generated in the processing spot (24) by the laser beam (14), and wherein a powdery coating material is applied to the molten pool (26) in the processing spot (24), comprising the steps of a) detecting the electromagnetic radiation emitted by the molten pool (26) as light (47) by means of an image detection device (40), wherein the brightness of the emitted light represents the intensity of the emitted electromagnetic radiation; b) forwarding the captured image information of the molten pool (26) to an image evaluation unit (42) and controlling and / or monitoring at least one parameter of the laser deposition welding process which influences the quality of the coating by means of a process control device (46) on the basis of the captured image information; is characterised by the further steps c) computationally determining the location data of at least one region (28) of the same intensity and / or of at least one region within a specific intensity interval in the captured image information to form a contour of the region; d) assigning at least one symmetrical, elliptical surface body (E) to the at least one region (28) of the same intensity and / or to the at least one region (28) within a specific intensity interval by approximating an ellipse to the contour of the region; e) identifying characteristic features of the geometric shape of the at least one symmetrical, elliptical surface body (E); f) storing the characteristic features of the at least one symmetrical, elliptical surface body as a data set in a data storage device (44); and g) detecting, controlling and / or monitoring the at least one parameter of the laser deposition welding process influencing the quality of the coating by means of the process control device (46) on the basis of the data of the characteristic features of the at least one symmetrical, elliptical surface body (E).

2. Method according to claim 1, characterised in that steps a) to g) are repeated at intervals.

3. Method according to claim 1 or 2, characterised in that the image information of the molten pool (26) detected in step a) is stored in a subsequent step a') in an image information storage device, in that steps a) and a') are repeated for several times, in that after a predetermined number of repetitions an averaging of the image information is carried out in a step a") and in that the subsequent process steps are carried out with this averaged image information.

4. Method according to claim 1, 2 or 3, characterised in that steps a) to f) are repeated at intervals and in that in step g) the data of the characteristic features of the at least one symmetrical surface body identified over a period of several intervals are first averaged.

5. Method according to claim 1, 2 or 3, characterised in that steps a) to c) are repeated at intervals, the location data of the at least one region (28) of equal intensity being averaged, and in that steps d) to g) are carried out on the basis of the at least one averaged region of equal intensity.

6. Method according to one of the preceding claims, characterised in that in step a) at least one spectral range of visible light and / or of ultraviolet light and / or of infrared light is detected.

7. Method according to claim 6, characterised in that steps a) to f) are carried out for a plurality of spectral ranges and in that step g) is carried out on the basis of the data of the characteristic features of the at least one symmetrical surface body (E) determined in the plurality of spectral ranges.

8. Device for optical quality control in laser deposition welding, having an image detection device (40), an image evaluation unit (42), a data storage device (44) and a process control device (46), designed for carrying out a method according to one of the preceding claims, wherein the image detection device (40) is designed to detect electromagnetic radiation emitted as light by a molten pool (26) formed in a processing spot (24), characterised in that the image evaluation unit (42) is adapted, - to determine, on the basis of the captured image information, the location data of at least one region (28) of the same intensity and / or of at least one region within a specific intensity interval in the captured image information to form a contour of the region (28), - to assign at least one symmetrical, elliptical surface body (E) to the at least one region (28) of the same intensity by approximating an ellipse to the contour of the region (28), - to determine characteristic features of the geometric shape of the at least one symmetrical, elliptical surface body (E), and - to store the characteristic features of the at least one symmetrical, elliptical surface body (E) as a data record in a data storage device (44), and in that the process control device (46) is designed to detect, control and / or monitor the at least one parameter of the laser deposition welding process which influences the quality of the coating by means of the data based on the characteristic features of the at least one symmetrical, elliptical surface body (E).

9. Device according to claim 8, characterised in that the image acquisition device is comprised of an electronic camera.

10. Device according to claim 8 or 9, characterised in that a decoupling mirror (15) is provided in the radiation path of the laser beam (14), which decouples the light (47) emitted along the radiation path of the laser beam (14), counter to its direction of propagation (A), from the processing spot (24) out of the radiation path of the laser beam (14) and guides it to the image acquisition device (40).